A lens of a conventional LED lamp is mounted on a heat radiation member. The lens is a plastic member, and the heat radiation member is made of metal. Because the deformation of the heat radiation member is very small, a deformation of a hook of the lens should be large so as to mount the lens on the heat radiation member. If a thickness of the hook of the lens is large, the deformation of the hook of the lens will be small. If the thickness of the hook of the lens is small, the hook of the lens will be broken when the lens is mounted. Moreover, because a thickness of a body of the lens is large, the hook of the lens shall have a predetermined thickness so as to meet requirements of injection molding. Thus, the lens of the conventional LED lamp is difficult to mount.